I'd bring it just because the Grand Canyon is so large. It won't get used as much as the other lenses, but it should get you some shots that you won't be able to get otherwise. It also depends on how long you'll be staying there and how many spots you'll be able to visit. If you are hiking/driving through large portions of the park and can get to many scenic spots, then the 70-200 is less useful.

I did a backpacking trip 2 decembers ago, hiking from the south rim, down to the canyon, then back up. I brought a 10-20 and a 70-200 on a crop body. I used the 10-20 70% of the time. Once down in the canyon, I was glad I had the extra reach for the Condors and Deer that we came across. But for being only up on the rim, I think a 17-40/24-70 is more than sufficient.

We spent three days at the Grand Canyon south rim and a day on the north rim last summer. I recommend taking the 70-200 along.

At that time we visited, I did not have a 70-200, but used a rented 100-400mm L for maybe 15% of my total shots, including some memorable shots of wildlife and some nice landscapes. I just took my standard zoom (EF-S 15-85mm) and 7D along for any hikes beyond a mile or two due to the weight and used the long lens from the overlooks and on short hikes.

I did a 10 day river trip through the Grand Canyon a few years ago and really didn't have the room for a 70-200 mm. I only had my 24-105mm on my 5D Mk2.. There were times (not on the river) I wished I had the 70-200 or larger for wildlife.

If you have the room then take the lens. If your backpacking, I would likely leave the lens home.

Packing for a trip to Vegas and Grand Canyon. Just wondering if it's worth taking along the 70-200. Trying to keep down the weight. Any thought?

Taking: 5D3, 17-40 f/4, and 24-70 f/2.8.

You might want to take the 70-200 for some sightseeing stuff in Vegas. I saw a shooter with one @ the Stratosphere taking shots along the strip. There is also the possibility of perhaps shooting some sights on a helicopter ride, where that range might be useful.